title: E4orf4, a novel adenovirus death factor that induces p53-independent apoptosis by a pathway that is not inhibited by zVAD-fmk.
abstract: In the absence of E1B, the 289-amino acid product of human adenovirus type 5 13S E1A induces p53-independent apoptosis by a mechanism that requires viral E4 gene products (Marcellus, R.C., J.C. Teodoro, T. Wu, D.E. Brough, G. Ketner, G.C. Shore, and P.E. Branton. 1996. J. Virol. 70:6207-6215) and involves a mechanism that includes activation of caspases (Boulakia, C.A., G. Chen, F.W. Ng, J. G. Teodoro, P.E. Branton, D.W. Nicholson, G.G. Poirier, and G.C. Shore. 1996. Oncogene. 12:529-535). Here, we show that one of the E4 products, E4orf4, is highly toxic upon expression in rodent cells regardless of the p53 status, and that this cytotoxicity is significantly overcome by coexpression with either Bcl-2 or Bcl-XL. Conditional expression of E4orf4 induces a cell death process that is characterized by apoptotic hallmark features, such as externalization of phosphatidylserine, loss of mitochondrial membrane potential, cytoplasmic vacuolation, condensation of chromatin, and internucleosomal DNA degradation. However, the wide-spectrum inhibitor of caspases, tetrapeptide zVAD-fmk, does not affect any of these apoptogenic manifestations, and does not alter the kinetics of E4orf4-induced cell death. Moreover, E4orf4 expression does not result in activation of the downstream effector caspase common to most apoptosis-inducing events, caspase-3 (CPP32). We conclude, therefore, that in the absence of E1A, E4orf4 is sufficient by itself to trigger a p53-independent apoptosis pathway that may operate independently of the known zVAD-inhibitable caspases, and that may involve an as yet uncharacterized mechanism.
authors.affiliation: Department of Biochemistry, McGill University, Montreal, Quebec, Canada H3G 1Y6. lavoie@medcor.mcgill.ca
authors.forename: J N
authors.initials: JN
authors.lastname: Lavoie
authors.forename: M
authors.initials: M
authors.lastname: Nguyen
authors.forename: R C
authors.initials: RC
authors.lastname: Marcellus
authors.forename: P E
authors.initials: PE
authors.lastname: Branton
authors.forename: G C
authors.initials: GC
authors.lastname: Shore
mesh_terms: D017504:Adenovirus E4 Proteins / Q000235:genetics / Q000502:physiology*; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D016466:CHO Cells; D053148:Caspase 3; D020169:Caspases; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000648:ultrastructure; D002467:Cell Nucleus / Q000648:ultrastructure; D006224:Cricetinae; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D053938:DNA Fragmentation; D004318:Doxycycline / Q000494:pharmacology; D015870:Gene Expression; D017930:Genes, Reporter; D019254:Genes, bcl-2; D007425:Intracellular Membranes / Q000502:physiology; D008564:Membrane Potentials; D051379:Mice; D008928:Mitochondria / Q000502:physiology; D010718:Phosphatidylserines / Q000032:analysis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000502:physiology*
chemical_list: D017504:Adenovirus E4 Proteins; D000590:Amino Acid Chloromethyl Ketones; D015853:Cysteine Proteinase Inhibitors; D010718:Phosphatidylserines; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases; D004318:Doxycycline